The present invention relates to a new and improved construction of apparatus for forming internal teeth at large workpieces at a gear shaping machine or gear shaper.
In its more specific aspects, the inventive apparatus for providing internal gear teeth at large workpieces at a gear shaping machine, comprises a machine bed upon which there are arranged a workpiece table for chucking or clamping a workpiece and an upright or stand. The workpiece table and stand are rotatable, relative to one another, about the workpiece axis and can be advanced or fed radially with respect thereto. The stand has guide means along which there can be moved to-and-fro a plunger by means of a plunger drive.
There are already known to the art gear shaping machines which, according to indexing techniques or part-rolling techniques, not only can fabricate external gear teeth, but also internal gear teeth, such as for instance spline teeth for shaft-hub connections as well as coupling or clutch teeth, with great accuracy and surface quality. To fabricate internal teeth the plunger, which carries the gear cutting tool, must have a cantilever, in other words, must protrude a certain distance away from the stand which is greater than one-half of the external diameter of the workpiece. In the case of workpieces of large diameter this causes difficulties, since if the plunger is extensively cantilevered, the machining forces exerted by the gear cutting tool, produce considerable bending moments at the plunger. Therefore, it is necessary to either tolerate appreciable deformations of the plunger, and thus, attendant impairment of the accuracy and surface quality of the internal teeth, or else the plunger must be structured to be particularly sturdy, and thus heavy, increasing the cost of the entire gear shaping machine and its operating speed is lowered. Hence, such machine then no longer operates economically when fabricating external gear teeth, and it is for this reason that it was necessary to produce the external teeth and the internal teeth of gears of large diameter at different machines. The necessity of rechucking or clamping the workpiece, when working at different machines, again is associated with the drawback that, not only are there present time losses, but especially there cannot be prevented loss in accuracy of the arrangement, especially axial alignment, between the internal teeth and the external teeth.